How They Work
TYPICAL SEPTIC SETTLING TANK
A septic system, properly installed and maintained is a good way to treat wastewater and to protect groundwater quality when municipal sewer service is not available. A typical septic system consists of two major parts, the septic tank and drainfield.
Waste from toilets, sinks, washing machines and showers enters the septic tank, which is a holding tank generally made of pre-cast concrete or fiberglass and is sized according to the estimated wastewater flow from a given-sized residence or business.
The septic tank is buried and watertight and separates the wastewater into three general components — solids or “sludge”, floatables or the “scum layer”, and a zone of relatively clear water. Anaerobic bacteria (able to live in an oxygen-free environment) perform the first treatment of the wastewater, generating gas that is vented through the vent stack of the building’s plumbing, and breaking the solids into a liquid form. The oxygen-free conditions inside the septic tank also deactivate some of the disease germs that are found in sewage.
From the septic tank, the liquid portion of the wastewater flows into the drainfield, which is generally a series of pipe and gravel or slotted panels (chambers) which are shallow buried slightly away from the tank. The drainfield provides soil based treatment of the sewage by allowing aerobic (oxygen-using) bacteria to continue deactivating the disease germs that remain in the wastewater. The soil is very important to the operation of your septic system because microbes found in the soil help digest or remove most contaminants from the wastewater before it reaches the groundwater.
In some areas where soil types such as clay layers or bedrock exist, or in areas where there is a shallow seasonal high water table, septic systems must be elevated above the ground surface (“mounded” systems). In some cases, advanced wastewater treatment systems that “aerate” or add oxygen to the wastewater may be required. This ensures the wastewater has sufficient permeable or unsaturated soil in order to provide adequate treatment before the remaining wastewater reaches the groundwater table and the underlying aquifer.
